Radio distance measuring system



Oct. 6, 1953 w. PALMER 2,654,884

RADIO DISTANCE MEASURING SYSTEM Filed Oct. 21, 1947 2 Shets-Sheet l lDISTANCE 0= Z l l 2 TRANSMITTER RECEIVER COUPLING TRANJMITTER RECEIVER(P) I (P) (u) (/N/T (U) um'r P 1 El IV 423 f 2 27 5 3 BA BAND BAND F/LTER FILTER 3 M0011 TOR FLTER /9 M0 WM TOR 39 -u) FREQUENCY v METERDIV/QER VELOCITY (BY 24/ INDICATOR -u) O FREQUENCY DIV/DER 37 k 3 2.9(By N) MVLTIPLIER PHASE (T/MEs M) \SHIFTER PHASE L DETECTOR RATE DEVICEVELOCITY IIEEIZI INVENTOR.

W/NsLow PALMER ATTORNEY REFERENCE 56 PHASE Oct. 6, 1953 w. PALMER 2,654,884

RADIO DISTANCE MEASURING SYSTEM Filed Oct. 21, 1947 2 Sheets-Sheet 2MOTOR HMPL lF/ER PHASE 7'0 BE MEASI/RED INVENTOR. E W/NSLOW PALMERPatented Oct. 6, 1953 RADIO DISTANCE MEASURING SYST-EM' Winsl0w Palmer,West Hempstead, N y-e-a'ssignor .to I The: fiperry Gorporation, .a.lcornoration of .Delaware Application OctOber ZI, 1947, Serial No.781,093

TI'his invention re'lates to-radio distance andvelocitydetermining-systems ,and,..more .particu- Liar iv Ito such-systems ,utjilizing. continuous Wave "transmissions. v

.Accordingly,.an..obj.ect of theinventionis to providemeansjtomeasurethe distance between Ltwo .points.

.Another object of'jthev invention, is to: determine lthe relativevelocity between two pointsat least one of which" is mobile.

Another object of the invention is to determine the distance between twopo,ints,,.byi transmitting discrete continuous wave signals from eachpoint and .comparingthem in phase, to thereby measure the.distance.in.j.terms. of the waivelengthotone .of saidsignals.

The. inventionfmay b.e. b.estunderstood by, first statingthreewelhknowni principles.

Principled Given a1 trainsmitterzat ,one location; radiating a.wavelandf av receiver responsive ,tothe wave at anothenlocation,thephaseof the wave at ,the receiver .is delayed, relative to the phase of thewave at .the transmitter,,by an dangl qual .to the distance 'fromithe'transmitterto' the receiver in wavelengths.

Principle II When tw'owaves are mixed and the heterodyne beat isextracted, if the higherfrequency componentwave isshiftedin phasethroughacertain angle, --the *beat frequency will shift ;in phase -throughthesame-angle and. in the same direction 5 if the lower frequencycomponent ,wave is shifted -in-phase through a certain angle, the

beat-frequency will-i shift through an equal angle but in the oppositedirection.

. Pm'ncipZe III However the proofs are. presentedin. the appli- I 'cantscopehdi'ng application No. 1132,5253, filed Qctob er,28, 1947.,nowBatent No..,2,611,127,-for Radio Position Determining Systems.

inventi n .w li. b eexpla ned. y m a s 50 the iolldwingsriecification inonne tion with the I drawin whichdssazschematic block diagliammi anembodiment of the invention.

The illustrated embodiment of the invention comprises range measuringequipment shown in :generalat l whichi-may be carriedron-armobilecraft,- and: which-"is-adaptedzto. cooperatezwith -a fixed-or-mobileitransponder at ardistance'tD to be measured;

The transponder' includes 1a transmitter 1.5

which may be of the: type whichrtransmitsga-:fre-

quency (10) either continuously, ;or"rin:response -to'an interrogatingsignal. iThe-range measuring setincludes a transmitter 5-20:whichatransrnits -;a frequency (u) The "transmitter-1201s. coupledthrough coupling unitsil :.to:an.-:.antenna:.22 rand also to a receiver5.23 :which receives E 500th frequencies (p)- and: (u') Intheftransponder :the transmitter i5 is coupled through.-.coup1ingL-unit1:6 to antenna-H andreceiver 18. The a receiver [:8 receives frequencies(p) and (u) and mixesrthemwandithe filter I I9 extracts the frequency(pa-u) "fromi the receiver output. "This frequency (p -ta)" isdivi'dedby frequency dividerjttand this divided frequency .(pw'u) is modulatedon carrier frequency (p) of transmitter I5' by'means of modulator 25.

The output of receiver 23 atithe station f I 1 is is connected to twofilters 26- and i 21, the first of which extracts the divided frequencymodulation (17PM) N .and;thesecon ro -:w1.1. chv derives-directly. thebeat 'I 'he divided fre quency .is multiplied to its originalfrequencyby multiplier 31 and it is compared in phase with the directlyderived frequency (12-40) in phase detector 28.

Phase detector;28,is arranged.tocgenerate. an. error ;,signal outputproportional to the :cosine of the difierence in-phase. This. errorsignal is. fed to a servo mechanism 29 whichis adapted to rotate phaseshifter '30,-'connected-between filter 2? and phase detector .28. rThezservo system changes the phase. of theoutputof-filter Zl, i. -e.,

ference and therefore-n0 errorzsignal. 1 11619311- brated indicator 3!geared-to the output shaft of servo: mechanism 29 *givesadirectindication of the range,.which;as=.will=. bewshown; is proportional b tphas shift.

If it is desired to obtain range indications on either position as inthe case of two mobile craft,

the transponder 2 may be eliminated and a range indicating set I, asmodified by the switch 39 connection, may be used at each locationthereby providing range indications of the distance at each location.

The switch 39 circuit comprises the addition of frequency dividingmechanism 32 which is connected to the output of filter 2'! and adaptedto divide it by another factor (1'). This divided frequency is thenmodulated upon the output of transmitter 29 by means of modulator 33,thus providing a phase reference modulation signal from each end of thedistance to be measured. The receiver at the other location would haveto have a filter responsive to gel instead of filter 26 which isresponsive to A direct reading of velocity may be obtained by connectinga frequency meter 34 between the output of filter 21 and the output ofmultiplier 31. This frequency meter will measure the rate of change ofphase, i. e., the difference in frequency between the output of filter21 and the frequency-multiplied output of filter 26, that is, theDoppler shift frequency. The indications of meter 34 must be calibratedin speed units based on the relation of the Doppler shift frequency tothe basic carrier frequency.

The velocity indication may also be obtained by mechanically measuringthe rate of change of range. This may be done by gearing a calibratedrate device 35 to the range indicator 3|.

The operation of the described system may be analyzed as follows:

Transmitter I5 generates a frequency (p) according to the followingequation:

e =E sin 211212 (a) Transmitter 20 generates a frequency (u) accordingto the following equation:

eu=Eu sin 21rut (b) The frequency (u) is received by receiver l8,delayed in phase proportionally to the time M and it appears in receiverI8 as follows:

where Distance Velocity of Propagation u =Eu sin 21m (t-M) (c) Thefrequency (p) is received at location I delayed in phase proportionallyto time M and it appears in the receiver 23 as:

ep =e sin 21m (t-M) (d) The signals represented by Equations a and c arecombined in receiver l8 and filter l9 producing a beat frequency of theform of Equation e:

This beat frequency is then divided by frequency divider 24 for purposesof identification. This division factor will be neglected as it is notnecessary for this analysis.

The beat signal represented by Equation e is modulated upon carrier (p)of transmitter producing a modulation term as follows:

4 This modulation is received by receiver 23 having been delayed inphase proportional to time M, in the following form:

em =Em cos [amt-M) 21ru(t2M) (g) and it is separated by filter 26multiplied by multiplier 31 and then applied to one input of phasedetector 28.

The other term applied to phase detector 28 is derived from receiver 23by filter 21 and it is the beat frequency received at location 1comprising Equation 1) and Equation d, of the form The signalscorresponding to Equations g and h are compared in phase in detector 23,measuring the difference phase angle 0, as follows:

Therefore 0 is proportional to M and therefore also to D where D ismeasured in wavelengths of frequency (u). (It) By way of example, assumethat the frequencies 21 and u of the transmitters l5 and 20 are and 101kilocycles per second respectively. Then the beat frequency is onekilocycle per second. The phase shift of the 101 kc. wave in going fromstation I to station 2 is 101000 X X 360= 36.36M degrees 5' mitter l5,and travels with it to station I, in-

curring the transit time delay M. Its phase delay in this passage is M200 X360=.072M degrees At station I, the 200 cycle signal is multipliedin the frequency multiplier 31 by the factor of five. This converts the200 cycle signal, delayed .072M degrees with respect to the transmitted200 cycle signal, to a one kilocycle signal, delayed 5 .072M=.36Mdegrees With respect to the one kilocycle signal from which it wasoriginally derived. This reproduced one kilocycle signal therefore has atotal phase delay of degrees with respect to what it would be if thedistance were zero.

The 100 kilocycle wave produced by the transmitter I5 is delayed 36Mdegrees in going from station 2 to station I. Accordingly, the onekilocycle beat signal in the output of receiver 23 is advanced 36Mdegrees with respect to what it would be if the distance were zero,because the lower frequency (100 kc.) wave is the one that has beendelayed.

The difference in phase between this signal, which was advanced 36Mdegrees, and the other, which was retarded 36.72M degrees, is 72.72Mdegrees, and is numerically equal to twice the egctgese phasedelay'ofthe- 1 kilocyclesignal"intravelling from station-1|:tozstationz; Withthe assumed frequencies, each degree of phasedifier ence between the twoone kilocycle signals at station! represent a round-:trip.transittime:of

the operation would be substantially as described,

exceptsthatfthe difference: in phase betweent'he onekilocyclelsignalsvatrstatiorr I would be 72M degrees, i. e. twice theone-way'phase delay of the 100 kil'ocycle signal.

Since-the phase difference between theone.

kilocycle signals is proportional toxthe distance, the rate of change ofthis phase difference is a measure of the velocity, which may beindicated by either the frequency meter 34 or the rate indicating device35.

The frequency divider 24 and the multiplier 3'! enable the beat signalproduced at station 2 to be transmitted on the carrier of transmitter 45without producing side bands that interfere with the beat signalproduced at station I.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departure from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Distance measuring equipment adapted to indicate the distance betweentwo locations comprising means at a first location to transmit a firstcontinuous wave signal, means at a second location to transmit a secondcontinuous wave signal of slightly different frequency, means at saidsecond location to receive both signals, means responsive to saidreceiving means to obtain a beat frequency between said signals, meansadapted to transmit said beat frequency as a modulation, means at saidfirst location to receive said first and second continuous wave signalsand said modulation, means responsive to said last named receiving meansto mix said first and second continuous wave signals and obtain the beatfrequency, means to compare in phase said directly derived difierencefrequency wave with said received modulation difference frequency wave,and means to indicate the distance between said locations as a functionof said phase difference.

2. A system for measuring distance between locations by radio meanscomprising means for transmitting a first continuous wave signal from afirst location, means for transmitting a second continuous wave signalfrom second location, means for receiving both of said signals at saidsecond location, means for heterodyning said signals to obtain a beatfrequency, means for transmitting signals proportional to said beatfrequency to said first location as a modulation of said secondcontinuous wave signal, means for receiving said first continuous wavesignals and said modulation at said first location, means forheterodyning said first and second continuous wave signals atzsaidsecond location to directly derive=- the beat frequen'cy, andl-means: for com-J paring in phase-the directly derived difference frequencywitl'i the difference frequency modu- 'latioii; said phasedifference'tl'iereby' givingan ins dication of tli'e distancebetween'said locations;

3.- Distance' measuring" equipment: adapted to measure the distancebetween two locations. comprisingmeans at -a first'location to transmita firstwave, means at a second location to transmit'asecondwave ofslightly differentxfrequency;

rneans' atsaid s'econd location to receive both of I said'waves; meansresponsiveto said receiving means to --0ttam a beat" frequencybetweensaid waves; means foroonverti'ng said beat frequencyto' adiiferentfrequency having a fixed relationship to said beatr'frequency; means fortransmittin -said converted" beat-frequency as a1 modulation on saidsecond? wave, means at said first lo'- cationto *receivesaid 'waves'andsaid modulation; means responsive tosaid-lastnamed receiving means 'tomix said waves and obtain the difference frequency, means forreconverting said modulation to said beat frequency, and means tocompare in phase said directly derived difference frequency with saidreceived reconverted modulation difference frequency.

4. The invention set forth in claim 3, wherein said means for convertingsaid beat frequency to a different frequency is a frequency divider, andsaid means for reconverting said modulation to said beat frequencyincludes a frequency multi- 'oiier.

5. A system for measuring distance between two points comprising meansfor transmitting waves of discrete frequency from the opposite ends ofthe distance to be measured, means for deriving a beat frequency of saidwaves from one location and, transmitting it as a modulation, means forderiving the same beat frequency of said waves at the second location,means for receiving said moduation beat frequency at said secondlocation, and means for comparing said directly derived beat frequencyand said modulation beat frequency in phase to thereby determine thedistance in terms of the wavelength of one of said signals.

6. A system for measuring distance and relative velocity between twopoints, at least one of which may be mobile, comprising means fortransmitting first waves of discrete frequency from the opposite ends ofthe distance to be measured, means for deriving a beat frequency of saidWaves at one location and transmitting it as a modulation, means forderiving the same beat frequency of said waves at the other location,means for receiving said modulation beat frequency at said otherlocation, means for measuring the phase difference of said directlyderived beat frequency and said modulation beat frequency, to therebydetermine the distance in terms of wavelength of one of said firstwaves, and means for measuring the rate of change of phase between themto thereby determine the relative velocity of said two points.

'7. Apparatus for measuring relative velocity between two pointscomprising means for transmitting first and second signals of differentfrequencies from the respective points, means for deriving a beatfrequency of said signals at one point and transmitting it as amodulation, means for deriving the same beat frequency of said signalsat the second point, means for receiving said modulation beat frequencyat said second location and measuring the rate of change of phase ofsaid directly derived beat frequency and said modulation beat frequencyto thereby determine the relative velocity of said points.

8. The invention set forth. in claim 7, wherein said means for measuringthe rate of change of phase of said directly derived beat frequency andsaid modulation beat frequency includes a frequency meter connected tomeasure the difference in frequency between said beat frequencies.

9. Apparatus for determining distance by radio means comprising meansfor transmitting signals from two separate locations, means for mixingsaid signals at said locations thereby obtaining certain modulationproducts, means for retransmitting said modulation products from one ofsaid locations, means for separately receiving said retransmittedmodulation products at the other of said locations and comparing them inphase with said locally derived modulation products, the phasedifference being alfunction of the distance between said locations.

WINSLOW PALMER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,750,668 Green Mar, 18, 1930 2,151,323 Hollmann Mar. 21, 19392,198,113 Holmes Apr. 23, 1940 2,248,727 Strobel July 8, 1941 2,259,982Alexanderson Oct. 21, 1941 2,268,587 Guanella Jan. 6, 1942 2,405,239'Seeley Aug. 6, 1946 2,412,003 Neufeld Dec. 3, 1946 2,435,615 VarianFeb. 10, 1948 2,470,787 Nosker May 24, 1949 FOREIGN PATENTS NumberCountry Date 581,568 Great Britain Oct. 17, 1946 OTHER REFERENCESHastings: Raydist-a Radio Navigation and Tracking System, Tele. Tech.,June 1947, pages 30-33 and 100403.

